The incidence of colorectal carcinoma is increasing in Japan. Malignant transformation in colorectal neoplasia is usually considered to be owing to adenoma-carcinoma sequence. Elucidation of the recent alteration in the biological properties of colorectal adenoma is sure to be useful to understand the recent increase of the colorectal carcinoma in Japan. We compared the histopathological feature, mitotic index, proliferative activity (Ki-67 labeling index), expression of glycoproteins such as MUC2 mucin, sialyl Lewis A (SLe(a)) and sialyl dimeric Lewis X (SLe(x)), and p53 protein overexpression, between 108 adenomas in the old period (Group A, from 1969 to 1985) and 140 adenomas in the recent period (Group B, from 1995 to 1998). The histological dysplasia, mitotic index and Ki-67 labeling index of the adenomas were significantly higher in Group B than in Group A. In contrast, the expression of MUC2 mucin, which is considered to be a differentiation factor of intestinal mucosal epithelium, was significantly reduced in Group B than in Group A. The SLe(a) and SLe(x) expressions showed no significant difference between them. The p53 expression showed no significant difference between them, except for the moderate dysplasia. These findings indicate that recent colorectal adenomas show more advanced degrees of histological dysplasia, more rapid growth, and reduced differentiation than colorectal adenomas, which developed at earlier times, and may be related with the recent high incidence of colorectal carcinoma in Japan.